In recent times, efforts have been increased to provide more safety for the inmates of vehicles. Numerous detailed investigations have been carried out in this respect in order to ascertain the conditions prevailing during collisions. Due to the findings thus obtined, a general reassessment of the facts and their application has led to a number of ameliorations such as the use of overall bumpers and crusher zones, the provision of more survival space, of rigid passenger compartments, of intravehicular obtuseness (= smooth interior), of splinter-proof glass, etc. The seats, too, were designed not only for maximum comfort but also for functional ease and operational stability. Further seat requirements include proper elasticity, vibration absorption, good aeration as well as sufficient heat retention and the occupant's freedom of motion despite the use of seat belts and moulded retaining rims.
In order to keep a person from being moved inside a crashing vehicle when the latter is coming to a standstill, this person must be firmly connected to the vehicle so as to be virtually a part thereof. Although the conventional belt does enforce the belt-fastened occupant's participation at the deceleration of the vehicle during an energy absorbing crash, there are certain limitations that still constitute safety hazards. For example, a sudden braking manoeuver may cause the shoulder strap or its attachment means to rapidly deteriorate even under moderate forces, as these are multiplied when the person's body presses heavily forward in a collision. Passive structures comprising belts that will automatically embrace any person who sits down in the car require reinforced fixing points at the respective doors and a tightening device for each seat, with the tightening and gappling of the belts being controlled through inertia-operated sensors.
It has been attempted to protect vehicle passengers be seats that will tilt from the normal fairly upright position into a reclined safety position upon violent deceleration of the vehicle. The known mechanisms for achieving this include relatively complicated lever systems and/or racks with linear or arcuate guide tracks fixed by the sides of a seat the bottom of which may thus move forwardly and upwardly in case of a crash, while its back may tilt backwardly. Where such pivoting movements may be freely brought about, they will be just as liberally cancelled by opposing accelerations so that the sitting person is thrown to and fro, e.g., with any stop and start under normal traffic conditions. Moreover, the conventional tilting systems depend solely on the force of braking or of crash inertia for causing the tilting motion which, therefore, may be far too late for adequate protection of the passenger even where he or she is, theoretically, the one to trigger a linkage for tilting prior to an impending collision. Worst of all, however, the pivoting movement of any such conventional seats is restrained to the longitudinal vehicle direction only, though it is a statistically established fact that straight head-on collisions are far less frequent than crashes involving at least one or the other of the vehicle corners. Consequently, not only will a conventional tilting seat -- even if it be pivoted in time -- offer insufficient protection due to the divergence between the collision direction and the line of the seat motion, but there will also be a considerable risk of clamping and jamming when the seat guide mechanism is subjected to lateral forces and torques, impeding or even preventing the vital reclining movement at the most critical time.